This invention relates to a polishing material used as free abrading particles for processing the surface of an object made of a metal or a non-metal such as ceramics and plastics.
The surface to be worked upon of a target object made of a metal or a non-metal such as ceramics and plastics is usually processed by using free abrading particles, or by causing slurry with an abrading material dispersed therein to be present between the surface of the target object and a polishing cloth and moving the target object and the polishing cloth relative to each other.
In such a process, a tape or a pad made of a woven cloth, an unwoven cloth, a flocked cloth, a raised cloth or a foamed material capable of taking in debris generated during the polishing process and elastically acting on the surface of the target object is used as the polishing cloth.
As disclosed in Japanese Patent Publications Tokkai 6-121923 and 2005-131711, furthermore, texturing slurry containing diamond clusters as abrading particles is being used. Diamond clusters mean a bunched combination of particles of artificial diamond obtained by an explosion shock method such as described in Japanese Patent Publications Tokkai 6-121923 and 2005-131711, by Eiji Oosawa in “Details of nano-diamond by oxygenless explosion method,” Journal of Toryu Gakkai, Vol. 47, No. 8 (August, 2003) at pages 414-417, by Kotaro Hanada in “Characteristics of diamond clusters and their application to solid lubrication,” ibid., Vol. 47, No. 8 (August, 2003) at pages 422-425, and by Masanori Araki in “Method of producing diamond and high-pressure technologies,” Technology Development News, No. 75 (January, 1998) at pages 3-4 (obtainable from internet address http://www.chuden.cojp/torikumi/news/pdf/075/NO7503.pdf).
Mechanism of texturing by diamond clusters will be explained first. Diamond clusters dispersed as polishing materials in slurry are carried inside the surface portion of the polishing cloth being pressed against the surface of the target object during the processing and are thereby pressed against the target object surface. Larger diamond clusters break up as they are carried in the surface portion of the polishing cloth and become diamond clusters of an appropriate size while being pressed against the target surface. These diamond clusters act on and polish the target surface while being carried inside the surface portion of the polishing cloth.
Since diamond clusters are formed with extremely small artificial diamond particles with primary particle diameter of 20 nm or smaller, it is considered possible to process the surface of a target object with a high level of accuracy.
There is currently a problem, however, that spots appear although texturing slurry having a polishing material comprising diamond clusters is used to process the surface of a target object. There remain fluctuations in the quality of the products after the processing, and it is not possible to obtain products with good reproducibility.
For the texturing of substrates for a magnetic hard disk, for example, slurry having a polishing material comprising diamond clusters dispersed therein is supplied to the surface of a rotating substrate (as an example of the aforementioned target object), a polishing tape (as an example of the aforementioned polishing cloth) is pressed to it and this tape is caused to travel so as to form approximately concentric circular texturing marks on the surface of the substrate. Texturing marks with a line density of 40 lines/μm or more can be formed by a process as described above but spots do appear, making the texturing marks locally unclear, causing fluctuations in the quality of the substrates after the processing. In other words, it is currently not possible to produce substrates of a specified quality level with good reproducibility.
Thus, there is currently a demand in the field of polishing technology for a new method of producing with good reproducibility products of a specified level of accuracy without spots.